Cardiac mass has been reported to be increased with age in humans and other mammalian species (I-9). The myocardial response to acute pressure or volume overload, however, is characterized by less new cardiac hypertrophy in the senescent heart (9-11). We have observed that left ventricular response to acute hemodynamic stress in terms of protein synthesis, RNA synthesis and immediate early gene expression (c-fos and c-jun) are less in old compared to young adult rat hearts (11). We postulate that the mechanisms responsible for the age associated cardiac hypertrophy and the decreased myocardial response to hemodynamic stress include an altered program of gene expression that occurs with aging. During the five year period, we will examine both changes in myocardial structure and changes in myocardial gene expression as influenced by age.